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Published February 16, 2006 | public
Journal Article

Alkylation of Phenol: A Mechanistic View


The current work utilizes the ab initio density functional theory (DFT) to develop a molecular level of the mechanistic understanding on the phenol alkylation in the presence of a cation-exchange resin catalyst, Amberlyst-15. The catalyst is modeled with the benzene sulfonic acid, and the effect of this acid on olefins such as isopropene (i-Pr) and tributene (t-Bu) in a phenol solution mimics the experimental condition. A neutral-pathway mechanism is established to account for early-stage high concentration of the phenolic ether observed in experiments. The mechanism involves an exothermic reaction between olefin and the benzene sulfonic acid to form ester followed by three reaction pathways leading to direct O-alkylation, o-C-alkylation, and p-C-alkylation. Our calculations conclude that O-alkylation to form the phenolic ether is the most energetically favorable in the neutral condition. An ionic rearrangement mechanism describes intramolecular migrations of the alkyl group from the phenolic ether to form C-alkylphenols, while the positively charged protonation significantly lowers transition barriers for these migrations. The ionic rearrangement mechanism accounts for high yields of o-C-alkylphenol and p-C-alkylphenol. Competition between the H atom and the alkyl R group at the substitutive site of the protonated ortho configuration is found to be the determining factor to the ortho/para ratio of C-alkylation products.

Additional Information

© 2006 American Chemical Society. Received 20 October 2005. Published online 24 January 2006. Published in print 1 February 2006. Financial support from ChevronTexaco is highly acknowledged. We would also like to thank all colleagues at the Power, Energy & Environmental Research Center (PEER) and Material and Processing Simulation Center (MSC) at Caltech for numerous helpful discussions. The computations were done mainly in MSC. The MSC is supported by grants from DoE, ASCI, ARO-MURI, ARO-DARPA, ONR-MURI, NIH, ONR, General Motors, ChevronTexaco, Seiko-Epson, Beckman Institute, and Asahi Kasei.

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